The present invention relates to an annular heat exchanger assembly. More particularly, the invention relates to such a heat exchanger assembly employable as a reheater section of a vapor generator suitable for use with a gas-cooled nuclear reactor in an electrical power generating facility.
A heat exchanger or vapor generator for use in a gas-cooled nuclear reactor provides an appropriate environment for the annular heat exchanger assembly of the present invention. Such an application particularly exemplifies problems which are overcome by the annular heat exchanger assembly of the invention. In this connection, gas-cooled nuclear reactors have been found to be a particularly efficient and economical means for producing electrical power from thermal energy developed within the reactor. Important operating conditions within such reactors include their operation at temperatures sufficiently high to directly produce steam at temperatures and pressures suitable for high efficiency operation of steam turbines.
In general, gas-cooled nuclear power plants circulate a primary coolant such as helium or carbon dioxide to withdraw thermal energy produced by the reactor; high temperatures are employed for greater efficiency. Steam for the operation of turbines is normally obtained by the transfer of heat from the primary coolant fluid to the secondary fluid of a watersteam system. This transfer of heat is commonly accomplished within a heat exchanger or vapor generator including various specialized sections permitting thermal energy withdrawn from the reactor to be utilized for the production of superheated steam.
When the heat exchanger or vapor generator is included within the same pressure vessel as the reactor itself, it is important that the size of the complete heat exchanger assembly be maintained at a minimum with the various heat exchanger sections being readily removable and replaceable through necessarily restricted openings in the containment vessel. It is also important, however, to maintain minimum gas flow resistance so that work expended in circulating the primary gas through the system may be minimized.
It is necessary to support the heat exchanger tubes at frequent intervals to protect them from flow-induced vibration earthquakes and their own dead weight loads. In the past, it had frequently been necessary to make these supports very large and strong because past heat exchanger design had limited the supports to a small number. As the tubes are internally cooled by the secondary fluid and the supports are maintained at a warmer temperature by the primary fluid, the tubes and the structures expand at different rates. In the prior art, complex arrangements of tubing have commonly been employed between heat exchanger sections to accommodate differential expansion. Because of other design problems, this tubing must usually be unheated which results in a decrease of efficiency for the heat exchanger.
Complying with design criteria of the type summarized above creates difficulties in the design of an effective heat exchanger or vapor generator for operation in applications such as gas-cooled nuclear reactors. Similar problems of complying with a limited space envelope and differential expansion while still providing an efficient unit are also encountered in other heat exchange applications where the heat exchanger assembly of the present invention may be employed to equal advantage.
Thus, there has been found to remain a need for an effective heat exchanger assembly having a compact annular configuration while providing effective heat exchange capabilities, maintaining minimum gas flow resistance and allowing for differential expansion without the use of unheated cross-over connections.